We have to remember when Brown Waller wrote his manuscript (before 1966) internet research was non-existent and research in major libraries was more limited than what we have today. He just couldn't get on the internet to do base research, then email a few libraries about their holdings. Back then, and I think you and Anne experienced this in South America, you had to literally go to every place you needed to search and do it by hand. So yes, if he is to be believed, he probably did go to over 20 libraries, historical societies, and archives, and travel all over the west to get what he did get. Especially so, in that he did not rely on many interviews for the book. He also did not have a plethora of 30 or more books on the subject to consult either. All he had was Horan and Kelly, and a couple of others to rely on as printed books on the subject.

Considering, he apparently had research experience, since he did complete a Thesis for his Master's degree. He was also single which gave him a lot of time on his hands. He worked at some point as a teacher, which probably gave him whole summers to research, and was in real estate, which probably meant that he was able to set his own hours.